Method and apparatus for providing tactile sensations

ABSTRACT

The present disclosure concerns a method and apparatus for the creation of an acoustic field for providing tactile sensations. More particularly, but not exclusively, this disclosure concerns a method and apparatus for the creation of an acoustic field providing tactile sensations for use with an interactive device. 
     The disclosure provides a method of generating a tactile sensation. The method comprises the steps of providing a plurality of acoustic transducers arranged to generate a predetermined distribution of pressure patterns, wherein the pressure patterns comprise a first region providing a first tactile sensation and a second region providing a second, different, tactile sensation.

FIELD

The subject matter described herein concerns a method and apparatus forthe creation of an acoustic field for providing tactile sensations. Moreparticularly, but not exclusively, this subject matter concerns a methodand apparatus for the creation of an acoustic field providing tactilesensations for use with an interactive device.

BACKGROUND

Various interactive haptic technologies exist, which provide a user orusers with tactile information or feedback, often in combination withvisual information displayed on an interactive screen. For example,previous haptic feedback devices include pins moving to physicallychange a deformable surface. A pen connected to an articulated arm maybe provided, as in the SensAble PHANTOM device. Alternatively, a usermay wear, for example in the form of a glove, one or more actuatorswhich are activated to provide haptic feedback to a user. However, ineach of these technologies, a user requires physical contact with adeformable surface, a pen, or a specially adapted glove. Suchrequirements reduce the usability and spontaneity which with a user mayinteract with a system.

Tactile sensations on human skin can be created by using a phased arrayof ultrasound transducers to exert an acoustic radiation force on atarget in mid-air. Ultrasound waves are transmitted by the transducers,with the phase emitted by each transducer adjusted such that the wavesarrive concurrently at the target point in order to maximise theacoustic radiation force exerted.

However, existing ultrasound haptic devices do not allow for theprovision of distinctive multiple localised feedback points in mid-air.A user is not able to distinguish between such multiple localisedfeedback points if they are separated only by a small distance.Therefore, there is also a limit to the resolution of the hapticfeedback devices which in turn limits how useful such devices can be.

Examples of when a high resolution haptic feedback device could beuseful include when a user cannot properly see a display because theyare driving, or when a user does not wish to touch a display becausethey have dirty hands. It would be advantageous to be able to provideuser feedback above such a surface in order to allow information to betransmitted via an additional, haptic, channel in parallel with or as analternative to the visual display.

The subject matter described herein seeks to mitigate theabove-mentioned problems.

SUMMARY

According to a first aspect of the subject matter described herein,there is provided a method of generating a tactile sensation comprisingthe steps of:

providing a plurality of acoustic transducers arranged to generate apredetermined distribution of pressure patterns,

wherein the pressure patterns comprise a first region providing a firsttactile sensation and a second region providing a second, different,tactile sensation.

That the first tactile sensation feels different from the second tactilesensation allows a user to distinguish between the first region andsecond region. Advantageously, a user being able to distinguish betweenthe first region and second region enables each region to be allocatedan individual meaning. For example, if the method is used to generatetactile sensations in relation to an interactive control device such asa music player control device, the first region may represent onecontrol element and the second region may represent a second, different,control element, for example a play/pause control element and a volumecontrol element respectively. The method provides a user with distincttactile sensations without requiring the user to wear or use any specialequipment.

The first tactile sensation and the second tactile sensation may beprovided simultaneously.

The acoustic transducers may be ultrasound transducers. The ultrasoundtransducers may be arranged to emit ultrasound at a frequency of 40 kHz.

The first region may comprise a focal point for a plurality of acousticwaves modulated at a first frequency, and the second region may comprisea focal point for a plurality of acoustic waves modulated at a second,different frequency. The acoustic waves may be modulated at a frequencybetween 0 Hz and half of the carrier frequency. The carrier frequencymay be 40 kHz. The acoustic waves may be modulated at a frequency from0.1 Hz to 500 Hz, and in some cases between 150 Hz and 250 Hz.Advantageously, modulating the acoustic waves at a frequency from 0.1 Hzto 500 Hz provides haptic feedback at the optimum frequencies fordetection by human skin, as the tactile receptors in skin are moresensitive to changes in skin deformation at these frequencies.

The first region may comprise a high pressure sub-region and a lowpressure sub-region. The second region may comprise a high pressuresub-region and a low pressure sub-region. The provision of high pressuresub-regions and low pressure sub-regions may increase the perceiveddifference between the first tactile sensation and second tactilesensation.

The method may be used to provide haptic feedback in association with aninteractive surface. An interactive surface may be a display screen withdirect interaction capability. For example, a user may interact with thedisplay screen through touch or touchless interaction. For example, thefirst region and second region may provide feedback points for a user ofan interactive surface. The provision of a first tactile sensation and asecond, different, tactile sensation allows meaning to be attributed tothe first and second tactile sensations.

The method may comprise each of the plurality of acoustic transducerscontributing to the first region and second region simultaneously.

The method may comprise providing an interactive screen, the first andsecond tactile sensation being created in close proximity to the screen,for example within a few centimetres of the screen, for example within 5cm of the screen, within 3 cm of the screen or within 1 cm of thescreen. The first and second tactile sensation may be created furtherfrom an interactive surface, for example from 4 cm to 20 cm of theinteractive surface, or up to multiple metres away from the interactivesurface. The tactile sensations may be provided such that a user canexperience the first and second tactile sensations whilst still beingable to see visual information being displayed on the screen. Theplurality of acoustic transducers may be provided on one side of aninteractive screen and the tactile sensation provided on the other sideof the interactive screen. The acoustic transducers may transmitpressure patterns through the interactive screen. The method maycomprise providing an object detection or tracking device. The objectdetection device may, for example, detect the presence of a user's handin front of a light switch and provide tactile feedback to indicate thelight is being turned on, or that the light is being dimmed. The methodmay comprise tracking a user's hand during interaction with aninteractive screen and modifying the pressure patterns transmitted bythe plurality of acoustic transducers in response to the movement of theuser's hand.

A system for providing tactile sensations comprising: a plurality ofacoustic transducers arranged to generate a predetermined distributionof pressure patterns,

wherein the pressure patterns comprise a first region providing a firsttactile sensation and a second region providing a second, different,tactile sensation.

The plurality of acoustic transducers may be arranged in a 2D array. Theplurality of transducers may be arranged in a 3D array.

The system may further comprise an interactive surface, for example aninteractive screen. The pressure patterns generated by the plurality ofacoustic transducers may be associated with visual information displayedon the interactive screen.

The system may include a tracking device. The tracking device may bearranged to track the movement of an object, for example part of a user,for example a hand. The output of the interactive screen may be changedin dependence on movement detected by the tracking device. The pressurepatterns generated by the plurality of acoustic transducers may bechanged in dependence on the output of the interactive screen. Such asystem may, for example, provide a control device for a music player.The interactive screen may display a play/pause control and a volumecontrol for the music player. The play/pause control may be associatedwith the first region. The volume control may be associated with thesecond region. A user is able to distinguish between the play/pausecontrol region and the volume control region by the different tactilesensations experienced at each region. The tracker device may detectmovement of a user's hand in the play/pause control region and providecontrol information to the music player accordingly. For example, agesture such as “tapping” in the play/pause region may result in themusic player playing or pausing musical output. The tracker device maydetect movement of a user's hand in the volume control region andprovide control information to the music player accordingly. Forexample, a gesture such as “sliding” in the volume control region mayresult in the volume of the musical output of the music player beingincreased or decreased. By providing different tactile sensations, thesystem allows a user to accurately place their hand or hands in theappropriate position for providing input to the interactive screen. Thesystem may be arranged to provide feedback to a user when the user'shands are located in the correct position to interact with the system.For example, when a user's finger is located in the play/pause controlregion or volume control region, a vibration may be transmitted.Alternatively the perceived strength or intensity of the feedback may beincreased. Tactile feedback may be provided when the control gesturesare completed and registered by the system.

In an alternative embodiment, the interactive screen may display mappingdata. The pressure patterns created by the plurality of acoustictransducers may represent an additional layer of data related to thedata shown on the interactive screen. For example, population data maybe represented by different tactile sensations. Alternatively oradditionally, the land type may be represented by different tactilesensations, for example the first tactile sensation representing landand the second, different, tactile sensation representing water.

In an alternative arrangement, the system may comprise a floor mat. Thefloor mat may be arranged to be walked over by a user. The first regionand second region may be used to provide different tactile sensations toa user walking over the floor mat. For example, the first region mayprovide a tactile sensation similar to that of walking through water.The second region may provide a tactile sensation similar to that ofwalking through sand. Such a system may be used to provide a virtualenvironment in a setting such as a theme park.

It will of course be appreciated that features described in relation toone aspect of the subject matter described herein may be incorporatedinto other aspects of the subject matter. For example, the method of thesubject matter may incorporate any of the features described withreference to the apparatus of the subject matter and vice versa.

DESCRIPTION OF THE DRAWINGS

Embodiments described herein will now be described by way of exampleonly with reference to the accompanying schematic drawings of which:

FIG. 1 shows a schematic view of a tactile feedback system according toa first embodiment;

FIG. 2 shows how pressure patterns may be multiplexed to providedifferent tactile sensations; and

FIG. 3 shows a flow diagram of calculations undertaken by a tactilefeedback system.

DETAILED DESCRIPTION

FIG. 1 shows a system 10 comprising a transducer array 12, a screen 14,a projector 16, a hand tracker 20, a PC 22, a driver circuit 24, and auser's hand 26. The transducer array 12 is located underneath the screen14 and arranged such that pressure patterns may be transmitted throughthe screen 14 to a region above the screen 14. In this particularembodiment, the transducer array comprises 320 muRata MA40S4Stransducers arranged in a 16×20 grid formation. Each transducer unit is10 mm in diameter and the transducers are positioned with no gap betweenthem in order to minimise the transducer array 12 footprint. Thetransducers produce a large amount of sound pressure (20 Pascals ofpressure at a distance of 30 cm) and have a wide angle of directivity(60 degrees). The transducers are arranged to transmit ultrasound wavesat a frequency of 40 kHz. The projector 16 is arranged to project visualinformation onto the screen 14 from above the screen 14 as shown. In analternative embodiment, the projector may be placed between thetransducer array and the screen, with the projection coming from belowthe screen.

A user interacts with this visual information and the movement andposition of the user's hand 26 is tracked by the hand tracker 20. Inthis particular embodiment, the hand tracker 20 is a Leap Motioncontroller arranged to provide the 3D coordinates of the user'sfingertips and palm at up to 200 frames per second. The system 10 iscontrolled by a PC 22, which sends control data to the projector 16,receives user data from the hand tracker 20, and controls the drivercircuit 24 for driving the transducer array 12. The PC 22 controls thedrive unit 24 such that a pressure pattern is created in the regionabove the transducer array 12. In response to the hand movements of auser, the PC 22 may drive the drive controller 24 to cause thetransducer array 12 to change the pressure pattern formed above thetransducer array 12.

In order to compute the amplitude and phase of the acoustic wave eachacoustic transducer must transmit for the desired pressure pattern to becreated. An algorithm adapted from that proposed by Gavrilov may beused, as set out in more detail below. A volumetric box is defined abovethe transducer array 12. Within the box, a plurality of control pointsare defined. The control points may represent points where a maximumpressure value is desired, or points where minimum pressure values aredesired. The pressure values are maximised or minimised by maximising orminimising the intensity of the ultrasound emitted by the transducerarray 12 which is incident at the control points.

An algorithm is used to model the outputs of each of the transducers inthe transducer array 12 required to obtain each of the desired pressurepatterns which may be created within the volume defined above thetransducer array 12. The algorithm may be split into three steps.

Firstly, the acoustic field generated by a single transducer iscalculated to create a large modelled volume. Thereby, the phase andamplitude at any point within the modelled volume may be determined byoffsetting the sample transducer for the position, phase, and amplitude,of each of the transducers in the real transducer array, and combiningthese values.

Secondly, the control points are defined in the 3D volume above thetransducer array such that the control points take on the requireddistribution. The control points may be points of maximum intensity orminimum intensity (also known as null points). In addition to a 3Dlocation, the desired modulation frequency of the maximum control pointsmay be specified. Therefore, a first control point may be defined with afirst modulation frequency, and second control point may be defined witha second, different, modulation frequency.

Thirdly, the optimal phases are calculated using a minimum norm solverso that the resulting acoustic field is as close as possible to thatspecified by the control points. There may be more than one solutionthat will create an optimal focusing to the control points, but somesolutions create a higher intensity than others. Solutions are thereforeiteratively generated to find the one that creates the highestintensity.

FIG. 3 shows a flow chart schematically representing an example methodof producing an acoustic field. The method begins at step 110, in whicha plurality of control points are defined. A control point is a pointpositioned in a space through which the acoustic field may propagate, atwhich the amplitude or phase of the acoustic field is to be controlled.A control point is a marker at a particular location. The distancebetween adjacent control points should be sufficient to enable the phaseof the sound waves of the acoustic field to shift from one of thecontrol points to match the next control point. In some embodiments theseparation distance may be equal to the wavelength of the sound waves ofthe acoustic field, for example a separation of 8.5 mm for a 40 kHzcarrier wave. In some embodiments, the separation distance may be equalto half the wavelength of the sound waves of the acoustic field. In someembodiments the separation may be greater than the wavelength of thesound waves of the acoustic field. The skilled person will appreciatethat other suitable separation distances could be used. The array oftransducers 12 is arranged to produce the acoustic field. The positionsof the control points relative to the array of transducers 12 isdetermined. The use of control points to control an acoustic field isknown from a paper entitled “The possibility of generating focal regionsof complex configurations in application to the problems of stimulationof human receptor structures by focused ultrasound”, L. R. Gavrilov,2008, Acoustical Physics Volume 54, Issue 2, pp 269-278, Print ISSN1063-7710.

In the embodiment described herein, the acoustic field is produced inair. However, in alternative embodiments the acoustic field may beproduced in another medium through which sound waves can pass, such aswater.

At step 112 amplitudes are assigned to the control points. The assignedamplitudes represent target amplitudes of the acoustic field at thecontrol points, which form a basis for modelling the acoustic field. Thecontrol points are assigned by a user; however, in other embodiments,the control points may be assigned by an automated process.

At step 114, an acoustic field is modelled for each control point.According to this embodiment, modelling the acoustic field at a controlpoint comprises modelling the acoustic field produced by a virtualtransducer directly below the control point in the plane of the realtransducer array, the initial amplitude and phase of the virtualtransducer being modelled such that the modelled acoustic field has theassigned amplitude at the control point. However, in some embodiments,alternative ways of modelling the acoustic field may be used, forexample, different arrangements of virtual transducers may be used, thatis one or more virtual transducers may be positioned directly below thecontrol point or may have a different spatial relationship to thecontrol point to produce the modelled acoustic field. In thisembodiment, step 114 comprises modelling the acoustic field separatelyfor each control point.

At step 116, a matrix is computed which contains elements whichrepresent, for each of the control points, the effect that producing themodelled acoustic field of step 114 having the assigned amplitude ofstep 12 with a particular phase at the control point has on theconsequential amplitude and phase of the modelled acoustic field at theother control points. In the first embodiment, the matrix computed atstep 116 is an N×N matrix where N equals the number of control pointsalthough other suitable forms of matrix will be apparent.

At step 118, eigenvectors of the matrix are determined. In the firstembodiment step 118 comprises determining right eigenvectors of thematrix, each eigenvector representing a set of phases and relativeamplitudes of the modelled acoustic field at the control points.

At step 120, a set of relative phases and amplitudes is selected byselecting one of the eigenvectors determined in step 118.

At step 122, initial phases and amplitudes to be output by theindividual transducers of the array of transducers are calculated. Theinitial phases and amplitudes are calculated such that they produce aresultant acoustic field with phases and amplitudes that correspond tothe phases and relative amplitudes of the selected set. In embodimentsof the subject matter described herein the term “correspond” may be usedto mean that the phases and amplitudes of the resultant acoustic fieldat the control points will be substantially equal to the phases andrelative amplitudes of the selected set, taking into account any errorsthat may be introduced as part of a regularisation step. Thus, thealgorithm according to embodiments of the subject matter describedherein may compute the phase delay and amplitude for the transducers inthe array that will create an acoustic field that best matches theassigned amplitudes of the control points.

At step 124, the transducers of the transducer array are operated suchthat the transducer array outputs acoustic waves having the initialamplitudes and phases which were calculated in step 122. In someembodiments, the transducers may be operated to continue to output oneor more acoustic waves. In some embodiments, the control points may bere-defined and the method may repeat with a different set of controlpoints. In some embodiments, the method may include the step ofcalculating eigenvalues of the matrix. The eigenvalues represent scalingfactors, some of which will be relatively high and some of which will berelatively low, in relation to each other. In some embodiments, themethod may comprise selecting a set of phases and relative amplitudeswith a relatively high corresponding eigenvalue as the selected set. Insome embodiments, the method may comprise selecting the set of phasesand relative amplitudes with the highest corresponding eigenvalue as theselected set. The eigenvalues define how the corresponding eigenvectorsscale when they are transformed by the matrix. That is, the eigenvaluesrepresent how much the relative amplitudes of the acoustic field at thecontrol points will scale up once the indirect contributions to theamplitude at each control point caused by producing an assignedamplitude at the other control points is taken into account. Therefore,finding a large eigenvalue indicates a corresponding set of relativeamplitudes and phases that make use of a large amount of constructiveinterference. Choosing a set of relative amplitudes and phases with acorresponding eigenvalue which is relatively high, taking into accountthe relative values of all the eigenvalues of the matrix, has anadvantage over choosing a relatively low eigenvalue, as it makes moreefficient use of the power output by the transducers. In someembodiments, the method may include computing the effect of producingthe assigned amplitude at one of the control points on the amplitude andphases at each of the other control points using a look-up functionwhich defines how the amplitude and phase of the acoustic waves varyspatially due to attenuation and propagation. In some embodiments inwhich a look-up function is used, the spatial variation of the phase ofthe sound waves due to attenuation and propagation is computed once fora particular transducer array, which decreases the time needed to modelthe acoustic field and the time needed to calculate the initialamplitude and phases of the transducers that will produce the phases andamplitudes of the resultant acoustic field. In some embodiments, themethod may include a regularisation step in which errors are introducedinto the initial amplitude and phase output by the transducers. Theadvantage of including a regularisation step is that this can improvethe power output efficiency of the array by increasing the averageamplitude of the transducers so that more of them are on at a higheramplitude. For example, to avoid a situation where one transducer is onat 100% and all of the others are on at 0.1%, the regularisation stepintroduces some errors in return for the average amplitude of thetransducers being raised to, say, 80%.

In some embodiments, the regularisation technique may be a weightedTikhonov regularisation. The advantage of using a weighted Tikhonovregularisation is that it has an easily specified matrix augmentation.In some embodiments, the power output by the transducer array may bescaled such that the transducer outputting the highest of the initialamplitudes operates at substantially full power. Scaling the poweroutput in this way has an advantage in that it results in the poweroutput of the transducer array being as high as possible for a given setof initial amplitudes, whilst maintaining the levels of the initialamplitudes, relative to each other. In some embodiments, the acousticwaves may be modulated at a frequency between 0 Hz and half of thecarrier frequency; in some embodiments the carrier frequency is 40 kHz.In some embodiments the acoustic waves may be modulated at a frequencybetween 0.1 Hz to 500 Hz, and in some cases between 150 Hz and 250 Hz.Modulating the acoustic waves at a frequency between 0.1 Hz to 500 Hzgives rise to an advantage of increasing the suitability of the methodfor use in haptic feedback applications, since tactile receptors inhuman skin are most sensitive to changes in skin deformation at thesefrequencies. In some embodiments, the positions of the control pointsmay be chosen to define parts of a virtual three-dimensional shape whichoccupies a volume in the acoustic field. In some embodiments, thecontrol points may lie on the edges of the shape or adjacent to theedges of the shape. In some embodiments, the control points may liewithin the volume of the shape. In some embodiments, the control pointsmay define the whole of the shape. In some embodiments the controlpoints may define part of the shape. In some embodiments, the controlpoints may define a shape to be felt by a user as part of a hapticfeedback system of which only the part of the shape with which the useris interacting may need to be defined. In some embodiments, the controlpoints may be divided into a first group of control points at which theacoustic field has a relatively high amplitude and a second group ofcontrol points at which the acoustic field has a relatively lowamplitude in comparison with the high amplitude. The control points'amplitude may be between the maximum and minimum; for example, somecontrol points may be at half amplitude. Some applications may have awide distribution of amplitudes throughout the control points; forexample, in order to vary the intensity of haptic feedback across aregion. In some embodiments, the edges of a virtual shape may be definedby the first group of control points. The control points in the secondgroup may each be arranged so as to be adjacent to a control point ofthe first group, such that a gradient in amplitude of the acoustic fieldis produced at the edge of a virtual shape. Providing a group of controlpoints at which the acoustic field has a relatively high amplitude and agroup of control points at which the acoustic field has a relatively lowamplitude to provide a gradient in amplitude of the acoustic field atthe edge of a virtual shape provides an advantage in haptic feedbackapplications since it produces a more detectable difference in amplitudeof the acoustic field, rendering the edge of the virtual shape moreeasily detectable by a user. At least some of the control points may bepositioned at points where an object intersects with a virtual shape. Atleast some of the control points may be positioned adjacent to thepoints of intersection. Positioning control points in the region ofpoints where an object such as a user's hand intersects a virtual shapeprovides the advantage that the acoustic field only needs to becontrolled at points on the virtual shape with which the object isinteracting, which enables higher amplitudes to be produced at thosecontrol points. The points where the object intersects with the virtualshape may be monitored in real time by an object tracker, and controlpoints may be positioned at different points in the acoustic field inresponse to the object position. In some embodiments, the number ofcontrol points may be at least 10 and preferably at least 50. A highernumber of control points enables the produced acoustic field to havemore points at which the amplitude can be controlled. This featureenables, for example, larger or more complicated 3-dimensional or2-dimensional virtual shapes to be defined, or where only part of avirtual shape is being defined, more detail may be represented on thatpart of the shape.

The control points are defined in 3D, and may lie in different planes.The control points may be positioned to create multiple high intensitypoints (control points) at different heights with respect to thetransducer array. Such control points may be utilised for example torepresent different points of user interaction or different informationvalues. In order to avoid having secondary maxima at unwanted points,null control points may be utilised. A null control point acts in theopposite way to a control point, and instruct the algorithm to generatezero amplitude at that point.

The human hand is not capable of detecting vibrations at 40 kHz.Therefore, the ultrasound transmissions of the transducers are modulatedin order to create vibrations that are detectable by the human hand. Theoptimum range for human detection is between 0.1 Hz to 500 Hz.

In example embodiments, modulating multiple focal points at differentfrequencies is achieved by time multiplexing scenes with differentnumbers of focal points. FIG. 2 shows a pressure pattern including twofocal points, A (dark circle) and B (light circle), each focal pointbeing a maximum intensity focal point. Focal point A is modulated at 200Hz and focal point B is modulated at 50 Hz. The different modulationfrequencies of focal point A and focal point B means a different tactilesensation will be experienced at each focal point. Four scenes aregenerated by the transducer array 12, one empty scene with no focalpoints, one scene with only focal point A, one scene with only focalpoint B, and one scene with both focal points A and B. The scenes arethen moved between as illustrated in FIG. 2. Firstly, at t=0 ms, nofocal points are generated, at t=5 ms, focal point A is generated, att=10 ms, no focal points are generated, at t=15 ms, focal point A isgenerated, at t=20 ms, focal point B is generated, at t=25 ms focalpoints A and B are generated, at t=30 ms, focal point B is generated, att=35 ms, focal points A and B are generated, and the sequence isrepeated. As can be seen in the figure, focal point A is being modulatedat a frequency of 200 Hz (on/off every 5 ms) and focal point B is beingmodulated at a frequency of 50 Hz (on/off every 20 ms). The amplitude ofa single focal point is greater than the amplitude of one of a pair offocal points. Therefore, after calculating the phases and amplitudes foreach scene, the amplitudes of the transducers is scaled such that theamplitudes of the focal points remains constant.

In order to reduce the attenuation of the ultrasound as it passesthrough the screen 14, it is preferred that an acoustically transparentmaterial is used to make the screen. Preferably the screen material isperforated in order to reduce the attenuation of ultrasound as it istransmitted through the screen.

In order to maximise the amplitude of multiple focal points, a distancethat is a multiple of the wavelength of the ultrasound should separatethe focal points. This allows individual sound waves to contributeconstructively to each focal point.

The method and system for providing tactile sensations may be used in anumber of different technologies. Such technologies include, but are notlimited to the following.

The method and system for providing tactile sensations can be used withinteractive displays, where mid-air gestures allow a user to interactwith the display. With the subject matter described herein, individualfeedback can be targeted to each finger of a user, thereby giving agreater sense of control and enabling the use of more reserved andprecise motions to provide commands to the display. The provision ofdifferent tactile sensations also allows a user to easily locatedifferent feedback regions of an interactive device.

The method and system for providing tactile sensations may be used tosupply a layer of non-visual information above a screen. Being able toprovide the tactile sensations a distance away from a screen allows auser to receive both visual and tactile information simultaneously. Asan example, when browsing a map, population data may be projected as aheat map into the air above the screen.

The method and system for providing tactile sensations may also be usedto guide and provide information to a user when a screen is not visibleto them, for example if the user is driving. The method and system forproviding tactile sensations may be used to guide the user to thelocation of an interactive element, for example a volume slider on amusic player. Feedback providing different sensations could guide a userto different elements of a music player, for example providing a strongfocal point above the main controls of a music player, and a weakerfeedback being provided above the volume slider. Alternatively, thedifferent feedback points may have different tactile sensations whenexperienced by a user.

The method and system may be used in a virtual reality gamingenvironment to provide tactile feedback to one or more players of agame.

Whilst the subject matter described herein has been described andillustrated with reference to particular embodiments, it will beappreciated by those of ordinary skill in the art that the subjectmatter described herein lends itself to many different variations notspecifically illustrated herein. By way of example only, certainpossible variations will now be described.

For example, ultrasound may be transmitted through an array of buttonsrather than a screen. An embodiment may comprise a keyboard with tactilefeedback being provided in the space above the keys, or a remote controldevice, so that information can be provided by waving a hand above thedevice. In an alternative embodiment, the tactile feedback system may beintegrated in the neck-rest of a car seat, to provide a user withtactile information on the neck corresponding to navigational cues suchas turn left or turn right. In such an arrangement, tactile feedback maybe provided to indicate the presence of another vehicle or object inproximity to a vehicle which the driver may not be able to see.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present inventions, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the subject matter that are described aspreferable, advantageous, convenient or the like are optional and do notlimit the scope of the independent claims. Moreover, it is to beunderstood that such optional integers or features, whilst of possiblebenefit in some embodiments of the subject matter, may not be desirable,and may therefore be absent, in other embodiments.

1. A method of generating a tactile sensation comprising the steps of: providing a plurality of acoustic transducers arranged to generate a predetermined distribution of pressure patterns, wherein the pressure patterns comprise a first region providing a first tactile sensation and a second region providing a second, different, tactile sensation.
 2. A method as claimed in claim 1, wherein the acoustic transducers are ultrasound transducers.
 3. A method as claimed in claim 1, wherein the first region comprises a focal point for a plurality of acoustic waves modulated at a first frequency, and the second region comprises a focal point for a plurality of acoustic waves modulated at a second, different, frequency.
 4. A method as claimed in claim 1, wherein the first region comprises a high pressure sub-region and a low pressure sub-region.
 5. A method as claimed in claim 1, wherein the second region comprises a high pressure sub-region and a low pressure sub-region.
 6. A method as claimed in claim 1, comprising providing an interactive surface, and the first region and second region providing feedback points for a user of the interactive surface.
 7. A method as claimed in claim 1, comprising an interactive screen, and the tactile sensation being created in close proximity to the screen.
 8. A method as claimed in claim 6, wherein the plurality of acoustic transducers may be provided on one side of the interactive surface and the tactile sensation provided on the other side of the interactive surface.
 9. A method as claimed in claim 1, comprising providing a tracking device, the method further comprising tracking an object during interaction with an interactive surface and modifying the pressure patterns transmitted by the plurality of acoustic transducers in response to the movement of the object.
 10. A system for providing tactile sensations comprising: a plurality of acoustic transducers arranged to generate a predetermined distribution of pressure patterns, wherein the pressure patterns comprise a first region providing a first tactile sensation and a second region providing a second, different, tactile sensation.
 11. A system as claimed in claim 10, wherein the plurality of acoustic transducers are arranged in a 2D array.
 12. A system as claimed in claim 10, wherein the plurality of acoustic transducers are arranged in a 3D array.
 13. A system as claimed in claim 10, further comprising an interactive surface.
 14. A system as claimed in claim 13, wherein the pressure patterns generated by the plurality of acoustic transducers are associated with visual information displayed on the interactive surface.
 15. A system as claimed in claim 10, further comprising a tracking device.
 16. A system as claimed in claim 13, wherein the interactive surface is a floor mat.
 17. A system as claimed in claim 13, wherein the interactive surface is a neck rest.
 18. A system as claimed in claim 13, wherein the interactive surface comprises an array of buttons. 